1. Field of the Invention
The present invention relates to a suspension device for a commercial vehicle and more particularly, to an improved suspension device including a leaf spring member and a pair of piston cylinder members operatively connected to the leaf spring member for preventing the vehicle from rolling and improving the feeling of entering the vehicle and handling of the vehicle.
2. Description of Related Art
Various types of suspension devices for a commercial vehicle are known in the art. Generally, most commercial vehicles including large sized trucks have an axle suspension device which includes an axle connected to right and left wheels, respectively, each axle including a spring member suspended from the vehicle frame. Such a spring member is either a parallel leaf spring or a cross leaf spring, but preferably a parallel leaf spring. Also, the parallel leaf spring has a number of advantages such as for example, it does not require an additional axle support since the parallel leaf spring supports the axle in a regular position and it is simple in structure.
However, this conventional leaf spring member suffers from a number of problems such as for example, it must be a large flexible spring since this spring has to transfer driving force, braking force, and centrifugal force to the frame from the wheels. Further, the conventional leaf spring does not exhibit an improved feeling of entering the vehicle and handling the vehicle, and it does not prevent the vehicle from rolling when the vehicle turns.
As shown in FIG. 4, the conventional suspension device including a parallel leaf spring member 58, comprises a main leaf 52 having a pair of eyes 50 disposed at opposing longitudinal ends thereof, a plurality of spring plates 54 of gradually increasing lengths and each having a large bending degree stacked down one-by-one, a pair of clip bands 56 for clipping the spring plates 54 to the main leaf 52 for forming a composite structure, an axle 60, and a plurality of U-bolts 62 for attaching the leaf spring 58 to the axle 60.
The leaf spring 58 is connected to a spring hanger 66 fixed to a vehicle frame 64 at one end and, at the other end thereof, is pivotally connected to a shackle 68 pivotally connected to the vehicle frame 64 for absorbing the change of a span of the leaf spring 58 when the leaf spring transforms so the suspension device is attempting to reduce impact and rolling of the vehicle in response to the rough road surface.
Even though the conventional suspension device provides a rubber bump stopper 72 fixed to the main leaf spring 52 for absorbing and buffering impact from the ground, since the rubber bump stopper 72 has a certain bump clearance, the conventional suspension device cannot prevent rolling, and does not improve feeling of entering the vehicle and handling of the vehicle whether the vehicle is fully loaded with goods or not.
Accordingly, in order to improve handling of the vehicle, if the conventional suspension device provides a narrow bump clearance, the feeling of entering the car decreases since the spring functions in lower degree or range of motion and the bump stopper 72 hits the frame 64 while the vehicle is driving on a rough road. On the contrary, if the conventional suspension device provides a wide bump clearance, the possibility of rolling of the vehicle is dangerously increased since when the vehicle turns, a rolling angle is large.